The freeze-fracture and -etch morphology of membranes of olfactory cilia differs considerably from that of the non-sensory cilia of the respiratory epithelium. These differences are presumably related to the different functions of both types of cilia, i.e., sensory olfactory ones versus respiratory motile ones. We plan to further characterize the microarchitecture of membranes of olfactory cilia with freeze-fracturing, -etching, -substitution, and -sectioning techniques, and with cytochemical and cytophysical probes. Cytochemical probes include ones which yield information about the membrane distribution of cholesterol, anionic lipids, triphosphonositides, glycoproteins and glycolipids. The probes are either visualized by characteristic membrane protuberances (freeze-fracture preparations) or by means of gold-conjugation (also in other preparations). The distribution of membrane-bound particles and probe-conjugated complexes will be studied as function of temperature (membrane thermotropic behavior) as well. Samples will furthermore be freeze-etched for different time periods; holes caused by etching reflect the stability of local membrane regions, and their sizes may be related to the microdomains detected with the above techniques. Finally, we will study the effect of odor exposure on membrane structure. Since odorants may induce local non-bilayer configurations, which can conceivably play a role in the receptive mechanism, we shall include pure lipid systems as comparison. Other controls include throughout respiratory cilia and the single primary cilium which precedes outgrowth of other olfactory cilia during ontogenesis of the olfactory receptor cell. This stage is included since cells with primary cilia are receptive to all administered odorants, and cells with other than primary cilia are receptive to a limited range of odorants. We believe that the proposed series of experiments should provide a thorough insight into the uniqueness of membranes of olfactory cilia.